To study the relationship between bites and kilocalories, a total of 83 people wore the Bite Counter for two weeks (Scisco, "Sources of Variance in Bite Count", PhD Dissertation, Psychology Dept, Clemson University, May 2012).
Ground truth kilocalories were measured using the
ASA24 dietary recall.
Over 4000 meals were evaluated, approximately 50 meals per person.
The following figures show the data for two participants. Each data point is one meal.
The bites-to-kilocalories correlation for the plot on the left is 0.4 and for the plot on the right is 0.7. Over 75% of participants had a correlation above 0.4.
While there is obviously noise in the kilocalorie-bite relationship for a single bite, due to the energy density of the food being eaten and natural variability in bite size, the relationship shows some stability at the meal level.

Bite Counter vs Physical Activity Monitors

There are a large variety of physical activity monitors,
including simple pedometers,
consumer-grade devices like the
Fitbit and
Nike's Fuel Band,
and professional-grade devices like the
Actigraph and
Actiwatch.
These devices provide a measure of energy expenditure.
The Bite Counter is similar but is the only device of its kind to
provide an automated measure of energy intake.

How good is the measure?
The plot below on the left shows the histogram of correlations for all 83 participants in the study described above.
To provide context, the plot below on the right shows a histogram of correlations found in a meta-study evaluation of 41 studies that compared energy expenditure as measured by physical activity monitors to doubly labeled water (Westerterp & Plasqui, 2007, "Physical Activity Assessment with Accelerometers: An Evaluation against Doubly Labeled Water", in Obesity, vol 15, pp 2371-2379).
As can be seen, the Bite Counter provides a measure of energy intake
comparable in quality to the measure of energy expenditure provided
by physical activity monitors.